First-principles modelling of the thermoelectric properties of n-type CaTiO3, SrTiO3 and BaTiO3

Abstract

Mitigating anthropogenic climate change requires a package of technologies including methods to improve the efficiency of energy-intensive transportation and industry. Thermoelectric (TE) power, which harnesses the Seebeck effect in a TE material to extract electrical energy from a temperature gradient, is a proven technology with the potential to meet this need. Oxide-based TEs are desirable for their low cost, high chemical stability and low toxicity, but are generally limited by a low electrical conductivity and high thermal conductivity. In this study, we employ a fully ab initio approach to predict the electrical and thermal transport and thermoelectric figure of merit ZT of the oxide perovskites CaTiO₃, SrTiO₃ and BaTiO₃ as a function of carrier concentration and temperature. We predict that carrier concentrations of n ≈ 10²¹ cm⁻³ are required to optimise the thermoelectric power factor, and that the piezoelectric scattering in rhombohedral BaTiO₃ limits the electrical conductivity compared to the other two systems. We find that the lattice thermal conductivity κ_latt is primarily determined by the structure type and chemical bonding through the phonon group velocities. We predict that CaTiO₃ and SrTiO₃ can achieve ZT > 1 at high temperature, and that the ZT of SrTiO₃ could be further enhanced by the impact of doping or alloying to obtain the required n on the κ_latt. The favourable comparison to experimental measurements suggests that this modelling approach has considerable predictive power, and could therefore serve as a valuable complement to experiments to identify new high-performance oxide TEs.